Editing Lower Palaeozoic rocks of the Craven Inliers - an excursion

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Three half-day excursions, mostly on public rights of way, in the three valleys where Lower Palaeozoic rocks are exposed: Chapel le Dale, Crummack Dale and Ribblesdale. There are car parks, toilets and services in Ingleton, Clapham, Stainforth and Horton in Ribblesdale.
 
Three half-day excursions, mostly on public rights of way, in the three valleys where Lower Palaeozoic rocks are exposed: Chapel le Dale, Crummack Dale and Ribblesdale. There are car parks, toilets and services in Ingleton, Clapham, Stainforth and Horton in Ribblesdale.
  
''Note ''Access to Arcow Quarry must be agreed with the quarry manager beforehand and will require safety helmets, protective footwear and insurance cover.
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''Note ''Access to Arcow Quarry must be agreed with the quarry manager beforehand (Tel: 01729 860202] and will require safety helmets, protective footwear and insurance cover.
  
 
== Maps ==
 
== Maps ==
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==== Locality 9, Central Crummack Dale [SD 773 708] ====
 
==== Locality 9, Central Crummack Dale [SD 773 708] ====
  
Follow the footpath northeast for 250 m, to where it crosses a stream that is coincident with the axis of the Studrigg–Studfold Syncline. Look west-northwest towards the unconformity on the west side of the valley, up the '''plunge''' direction of the fold; the '''strike''' of the sandstone beds (Austwick Formation) can be seen to swing round in the fold closure. The erosion-resistant sandstones form a palaeotopographic high point on the Sub-Carboniferous unconformity which has risen more than 100 m from Nappa Scars. About 300 m northeastwards along the footpath, the thick-bedded turbidite sandstones on the northern limb of the syncline can be examined. Towards Austwick Beck [SD 778 715], the ground is extensively drift covered, but to the east on Hunterstye, another major fold, the Crummack Anticline, can be seen. Join the lane and continue northwards to Locality 10.
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Follow the footpath northeast for 250 m, to where it crosses a stream that is coincident with the axis of the Studrigg–Studfold Syncline. Look west-northwest towards the unconformity on the west side of the valley, up the plunge direction of the fold; the strike of the sandstone beds (Austwick Formation) can be seen to swing round in the fold closure. The erosion-resistant sandstones form a palaeotopographic high point on the Sub-Carboniferous unconformity which has risen more than too m from Nappa Scars. About Soo m northeastwards along the footpath, the thick-bedded turbidite sandstones on the northern limb of the syncline can be examined. Towards Austwick Beck [SD 778 715], the ground is extensively drift covered, but to the east on Hunterstye, another major fold, the Crummack Anticline, can be seen. Join the lane and continue northwards to Locality 10.
  
 
==== Locality 10, Moughton Whetstone Hole [SD 784 719] ====
 
==== Locality 10, Moughton Whetstone Hole [SD 784 719] ====
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Where the footpath leaves the enclosed farmland is Moughton Whetstone Hole. Adjacent to the stream, the ground is littered with fragments of dark red and green banded rock, the remnants of a bygone enterprise that worked the Austwick Formation sandstone for whet, or sharpening, stones. The dark red and green banding phenomenon, known as liesegang rings, results from the weathering of iron oxides in the sandstone. This occurred during the Devonian and early Carboniferous when the deformed Lower Palaeozoic rocks were part of a continental area and subjected to subaerial erosion. In some fragments laminae (bedding) are preserved, crosscut by the younger liesegang rings. The colour banded rock can be seen ''in situ ''on Capple Bank, in small exposures north of the footpath, next to the wall.
 
Where the footpath leaves the enclosed farmland is Moughton Whetstone Hole. Adjacent to the stream, the ground is littered with fragments of dark red and green banded rock, the remnants of a bygone enterprise that worked the Austwick Formation sandstone for whet, or sharpening, stones. The dark red and green banding phenomenon, known as liesegang rings, results from the weathering of iron oxides in the sandstone. This occurred during the Devonian and early Carboniferous when the deformed Lower Palaeozoic rocks were part of a continental area and subjected to subaerial erosion. In some fragments laminae (bedding) are preserved, crosscut by the younger liesegang rings. The colour banded rock can be seen ''in situ ''on Capple Bank, in small exposures north of the footpath, next to the wall.
  
Return down the lane towards Wharfe. Southward-dipping Austwick Formation can be seen below the unconformity on Studrigg [SD 781 708]. The axis of the Studrigg–Studfold Syncline is crossed where the lane turns sharply to the right [SD 777 705]. Northward-dipping rocks can be seen next to the ford in Austwick Beck where Silurian 'flags' have been used to construct a clapper bridge. The lane to Wharfe follows the foot of the escarpment formed by northward-dipping Austwick Formation sandstone. There is a choice of footpaths to return to Austwick and Clapham.
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Return down the lane towards Wharfe. Southward-dipping Austwick Formation can be seen below the unconformity on Studrigg [SD 781 708] The axis of the Studrigg–Studfold Syncline is crossed where the lane turns sharply to the right [SD 777 705]
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Northward-dipping rocks can be seen next to the ford in Austwick Beck where Silurian 'flags' have been used to construct a clapper bridge. The lane to Wharfe follows the foot of the escarpment formed by northward-dipping Austwick Formation sandstone. There is a choice of footpaths to return to Austwick and Clapham.
  
 
=== Ribblesdale ===
 
=== Ribblesdale ===
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Younger parts of the Silurian succession are preserved in Ribblesdale because the main synclinal axis plunges east-southeast.
 
Younger parts of the Silurian succession are preserved in Ribblesdale because the main synclinal axis plunges east-southeast.
  
The stratigraphy, sedimentology and structure of the Wenlock and Ludlow parts of the Windermere Group and the Sub-Carboniferous unconformity are superby exposed in two quarries less than 1 km apart ([[:File:YGS_YORKROCK_FIG_01_01.jpg|Figure 1.1]]).
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The stratigraphy, sedimentology and structure of the Wenlock and Ludlow parts of the Windermere Group and the Sub-Carboniferous unconformity are superby exposed in two quarries less than 1 km apart ([[:File:YGS_YORKROCK_FIG_01_01.jpg|Figure 1.1]]).
  
 
==== Locality 11, Arcow Quarry [SD 802 705] ====
 
==== Locality 11, Arcow Quarry [SD 802 705] ====
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Access to the quarry should have been arranged beforehand (see logistics).
 
Access to the quarry should have been arranged beforehand (see logistics).
  
The roadstone quarry is in the Austwick, Arcow and Horton Formations on the southward-dipping, northern limb of the Studrigg—Studfold Syncline. The structure is most clearly seen from the east side of the quarry [SD 804 705]
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The roadstone quarry is in the Austwick, Arcow and Horton Formations on the southward-dipping, northern limb of the StudriggStudfold Syncline. The structure is most clearly seen from the east side ofthe quarry [SD 804 705]
  
 
On the north side there is an east-southeast plunging anticline, a parasitic fold on the limb of the main syncline. The anticline and most of the quarry are in the Austwick Formation, an interbedded succession of turbidite sandstone and siltstone. On the south side of the quarry the overlying Arcow and Horton Formations are present. The succession can be examined in detail on one of the benches part way up the west side of the quarry.
 
On the north side there is an east-southeast plunging anticline, a parasitic fold on the limb of the main syncline. The anticline and most of the quarry are in the Austwick Formation, an interbedded succession of turbidite sandstone and siltstone. On the south side of the quarry the overlying Arcow and Horton Formations are present. The succession can be examined in detail on one of the benches part way up the west side of the quarry.
  
The sandstone units consist of parallel-bedded fine to medium grained turbidites up to 2 m thick. Some of the thicker beds have coarse bases, consisting of ill-sorted quartz, feldspar and rock fragments with a clay matrix. Sole structures, mostly '''flute casts''', on the base of some beds indicate turbidity currents flowing from an east-southeast direction. Ripple marks on the top of the sandstones, however, show current reworking from the west-southwest. The sandstones pass gradationally upwards into overlying dark-grey, parallel-laminated siltstones containing a few thin mudstone and siltstone turbidites. Graptolites of Wenlock age are present. Approximately 20 m of siltstone separate the youngest sandstone unit from the overlying Arcow Formation.
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The sandstone units consist of parallel-bedded fine to medium grained turbidites up to 2 m thick. Some of the thicker beds have coarse bases, consisting of ill-sorted quartz, feldspar and rock fragments with a clay matrix. Sole structures, mostly flute casts, on the base of some beds indicate turbidity currents flowing from an east-southeast direction. Ripple marks on the top of the sandstones, however, show current reworking from the west-southwest. The sandstones pass gradationally upwards into overlying dark-grey, parallel-laminated siltstones containing a few thin mudstone and siltstone turbidites. Graptolites of Wenlock age are present. Approximately 20 m of siltstone separate the youngest sandstone unit from the overlying Arcow Formation.
  
The Arcow Formation comprises 9 m of medium to light-grey, weakly bedded, calcareous siltstone. The basal metre is thin bedded and some beds are ripple '''cross-laminated'''. Extensive '''bioturbation''' has destroyed most of the bedding. It contains a sparse shelly fauna dominated by '''orthocones'''. '''Benthonic''' fauna and bioturbation indicate an oxygenated depositional environment, contrasting with anoxic conditions for the beds above and below. There is a 2 m gradational passage into the overlying Horton Formation.
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The Arcow Formation comprises 9 m of medium to light-grey, weakly bedded, calcareous siltstone. The basal metre is thin bedded and some beds are ripple cross-laminated. Extensive bioturbation has destroyed most of the bedding. It contains a sparse shelly fauna dominated by orthocones. Benthonic fauna and bioturbation indicate an oxygenated depositional environment, contrasting with anoxic conditions for the beds above and below. There is a 2 m gradational passage into the overlying Horton Formation.
  
The Horton Formation consists of dark-grey, parallel-laminated siltstone that is sandy and calcareous in part. Calcareous nodules occur near the base, often in layers. Only the oldest part of the 700 m thick succession, with poorly preserved Ludlow graptolites, is exposed in the quarry.
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The Horton Formation consists of dark-grey, parallel-laminated siltstone that is sandy and calcareous in part. Calcareous nodules occur near the base, often in layers. Only the oldest part of the 700 m thick succession, with poorly preserved Ludlow graptolites, is exposed in the quarry.
  
 
==== Locality 12, Combs Quarry, Foredale [SD 800 701] ====
 
==== Locality 12, Combs Quarry, Foredale [SD 800 701] ====

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